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m in (-oo:+oo)
-12 = m+3*m+8 // - m+3*m+8
-m-(3*m)-12-8 = 0
-m-3*m-12-8 = 0
-4*m-20 = 0 // + 20
-4*m = 20 // : -4
m = 20/(-4)
m = -5
m = -5
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